1. Field of the Invention
The present invention relates to a method for ascertaining an actuating position of a vehicle part that can be moved by means of an electric actuating motor via an actuating mechanism. The invention also relates to an associated actuating device for automatically moving the vehicle part. The vehicle part to be moved is, in particular, a vehicle window. The actuating device is, in particular, an electric motor driven window regulator, preferably a cable window regulator.
2. Description of the Background Art
A conventional cable window regulator usually has an electric actuating motor whose motor shaft is coupled to the vehicle window to be moved. The actuating motor is typically driven by a control unit, e.g. composed of a microcontroller. The current actuating position of the window generally is calculated continuously by the control unit during each actuating operation, in particular in order to be able to move to specific window positions in a targeted way.
The actuating position of the window usually is derived by the control unit from the angle of rotation through which the actuating motor rotates during the actuation process. This angle of rotation and the speed of the motor shaft that can be derived therefrom are often measured directly. A Hall sensor that works together with a ring magnet attached to the motor shaft in a rotationally fixed manner is typically used for this purpose. Alternatively, the angle of rotation of the motor shaft can also be ascertained from the motor current, in particular by counting so-called current ripples.
It is disadvantageous that the “logical actuating position” of the vehicle window derived from the angle of rotation of the motor shaft usually matches the actual “mechanical” actuating position only to within a certain error. The reason for this, in particular, is that the actuating mechanism coupling the motor shaft to the window always has a certain system tolerance (also called “system slack”), as a result of which the window is only “soft-coupled” to the motor shaft.
A relatively high system tolerance normally occurs in cable window regulators. The system tolerance here is substantially dependent on the setting properties of the control cable, and for this reason is also referred to as “cable slack.”
The system slack of a cable window regulator manifests itself to an especially marked degree during a reversal of the actuating direction, especially since the control cable here must be rewound from the state in which it is tensioned in the original direction until a sufficient tension has been established in the opposite direction in the control cable. During the rewinding, the motor shaft moves while the window to be moved remains stationary.
In the conventional methods for ascertaining the (logical) window position from Hall signal pulses or the counting of current ripples, the process of overcoming the system slack consequently results in a counting of pulses that are not correlated with a corresponding movement of the window. The logical window position is thus variable relative to the mechanical window position, which manifests itself as errors in approaching the desired window position. Since the count error associated with the system slack changes its sign with the actuating direction, a desired actuating position is approached differently from different actuating directions.
The error-prone positioning of the window by conventional cable window regulators is a substantial disadvantage for the so-called short-stroke function in particular, in which the window is moved out of the upper door seal of a frameless vehicle door in order to permit the vehicle door to be opened without resistance. Vehicle manufacturers often place tight limits on the short-stroke motion. This is intended to ensure that the window travels completely out of the window seal on the one hand, but on the other hand the window is not open too wide after the short stroke, especially since additional safety precautions, such as automatic pinch protection, are otherwise required in some cases by the applicable legal requirements for the reverse motion of the window.
However, a precise approach is desirable for other actuating positions of a window as well, in particular for approaching the upper or lower pre-shutoff points, where the window normally is stopped before actually reaching the (upper or lower) blocked state. Moreover, precise positioning of a window is also desirable when approaching the so-called RELAN (Relax After Normalization) point, for example. This term is understood to mean the particular window position to which the window is often moved back after adjustment travel to the upper or lower blocked state in order to release the tension in the actuating mechanism.
Apart from this, an ascertainment of the actuating position corrected for the influence of the system slack is also beneficial for other window regulator types as well as other actuating devices in a vehicle, in particular seat adjustments, door and roof actuators, etc.
Because the system slack in conventional cable window regulators changes primarily due to the age-related setting properties of the cable system, a cable tensioner is sometimes used in such window regulators that irreversibly adjusts itself in the event of elongation of the cable path, and thereby compensates for the age-related increase in the system slack. However, such a cable tensioner requires additional material and assembly expense, which it is desirable to avoid.
A method for numerical compensation of the system slack in controlling the motion of a window is known from DE 196 32 139 C1, which corresponds to U.S. Pat. No. 6,166,508, and which is incorporated herein by reference. Here, the period of the motor rotation is sensed in a time-resolved manner during an actuation process using motion signals of the actuating motor or motor shaft. An initial no-load phase of the actuation process, during which the motor shaft rotates while overcoming the system slack without motion of the vehicle part, is identified by comparison of the time-dependent period with a threshold. During the course of the prior art method, an actuating position measure for the actuating position of the window corrected by the motor rotation during the no-load phase is ascertained by the means that all motion signals before the threshold is exceeded are assigned to the system slack and accordingly are not evaluated for determining the actuating position measure.